Immunity

Skin

The skin is a non-specific primary defense and the main one.

The upper layer of the skin is called the epidermis which consists of layers of cells.

At the bottom of the epidermis you get cells called keratinocytes which divide by mitosis.

Then they move to the upper layer of the skin and as they do they dry out and the cytoplasm is replaced with keratin.

This eventually kills the cells and they die at the top of the epidermis.

Layer of dead cells at the top of your epidermis acts as an effective layer-blocking pathogen entry into skin/tissue.

Blood clotting and skin repair:

if the skin is breached by a cut or other injury, platelets in the the blood plasma will trigger the formation of a blood clot (and eventually a scab) to seal the wound.

This helps to prevent pathogens entering the body.

Mucous membrane:

Surfaces of the respiratory system, such as the nose, trachea and the bronchi, are lined with mucous membranes. These contain goblet cells, which secrete sticky mucus that traps microbes.

Cilliated epithelial cells help 'waft' the mucus up your throat so it can be swallowed and goes to the stomach (PH 1-2). The stomach is acidic which kills any pathogens trapped in the mucus.

Also, cilliated epithelial cells sweep out the mucus which preventing pathogens from entering the lungs.

Tear enzymes- help to digest pathogens before entering out eyes (as eyes contain living cells)

Ear wax traps pathogens

Female reproductive system

Vagina:acidic

Mucus plug in cervix

Inflammation:

Deals with infected tissues- if tissue is red/swell. Mast cells produce histomine which increase flow of blood so more white blood cells gets to the site of infection quicker.

They also increase leakiness of capillaries therefore, white blood cells can come out of capillaries into affected tissues and 'mop' up any pathogens.

1) The phagocyte is attracted to the pathogen by chemical products of the pathogen.

2) The phagocyte has several receptors on its cell-surface membrane that attach to chemicals on the surface of the pathogen.

3) They engulf the pathogen to form a vesicle, known as a phagosome

4) Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium

5) the lysosomes release their lysozymes into the phagosome, where they destroy ingested bacteria by hydrolyse of their cell walls. 

6) the hydrolysis products of the beacterium are absorbed by the phagocyte.

Mainly neutrophills

Macrophages present the pathogens antigens for lymphocytes

The human body has a range of defences to protect itself from pathogens. some are general and immediate defences like the skin forming a barrier to the entry of pathogens and phagocytosis.

Others are more specific, less rapid but longer lasting. these responses involve a type of white blood cell called a lymphocyte and take 2 forms:

• Cell-mediated responses involving T lymphocytes
• Humoral responses involving B lymphocytes 

Each cell has a specific protein molecule on its surface - complex tertiary structure. This allows the body to tell the difference between self and non-self.

To defend the body from invasion by foreign material, lymphocytes must be able to distinguish the body's own cells and molecules (sefl) from those that are foreign (non-self).

Each cell, self or non-self, has specific molecules on its surface that identify it. The proteins are important because they have a highly specific tertiary structure. It is this variety of specific 3-D  structure that distinguishes one cell from another. These protein molecules (antigens) allow the immune system to identify:

• Pathogens, e.g. HIV, viruses, fungi and bacteria. Pathogens are organisms that cause disease.
• Non-self material such as cells from other organisms of the same species.
• Toxins (antigens themselves).
• Abnormal body cells such as cancer cells

Implications for the humans who have had tissue or organ transplants. the immune responce recognises these as non-self even though they have come from individuals of the same species, therefore it attempts to destroy the transplant. To minimise tissue rejections, donar tissues for transplant are normally matched as closely as possible to those of the recipient. best matches come from relatives. Immunosuppressant drugs are often administered to reduce the level of the immune responce that still occurs.

There are probably ten million different lymphocutes present at any time, there is a high probability that, when a pathogen enters the body, one of these lymphocytes will hve a protein on its surface that is complementary to one of the proteins of the pathogen- clonal selection

In the fetus, lymphocytes are consantly colliding with other cells, however, infection in the fetus is rare because it's protected from the outside world by the mother and the placenta.

Lymphocytes will therfore collide with body self cells, some will have receptors that exactly fit those of the body's own cells- they die/supressed.

the remaining lymphocytes are those that might fit foreign material (non-self), therefore only respond to them

in adults, lymphocytes produced in the bone marrow initially only encounter self-antigens.

Antigens are molecules that can generate an immune response when detected by the body.

antigens are usually proteins that are part of the cell-surface membranes or cell walls of invading cells, e.g. microorganisms, or cancer cells.

the presence of an antigen triggers the production of an antibody as part of the body's defence system.

antigens that aren't normally found in the body are referred to as foreign antigens and these that the immune responce usually responds to.

Immune responses such as phagocytosis are non-specific and occur whatever the infection.

The body also has specific responses that react to specific antigens, slower in action at first but they can provide long term immunity.

Lyphocytes are a type of white blood cell and both cells are made in the Bone marrow and only the B - Lymphocytes mature in the Bone marrow, whereas the T Lymphocytes travel to the Thymus gland where they mature. Two types each with it's own role in the immune response:

• B lymphocytes (B cells) they mature in the bone marrow. Associated with humoral immunity, that is, immunity involving antibodies that are present in the body fluids, or 'humour' such as blood plasma.
• T lymphocytes (T cells) they mature in the thymus gland. Associated with cell mediated immunity, atht is immunity involving body cells. It has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes- this activates the T-cell.

Produced by the introduction of antibodies from an outside source.

Type of immunity you get from being given antibodies made by a different organism- your immune system doesn't produce any antibodies of its own- two types:

1. Natural- this is when a baby becomes immune due to the antibodies it recieves from its mother, through the placenta and in breast milk

2. Artificial- when you become immune after being injected with antibodies from someone else. e.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations.

Type if immunity you get when your immune system makes its own antibodies after being stimulated by an antigen. There are two types

1) Natural- when you become immune after catching a disease

2) when you become immune after you have been given a vaccination containing a harmless dose of antigen